Global navigation satellite systems often employ augmentation data from sources outside the satellite based navigation system to enhance the accuracy of the system; for example, Global Positioning System (GPS) altitude data is generally not approved as a primary means of navigation because of the lack of observability in the vertical direction. Civilian users can utilize global navigation satellite system augmentation data to overcome this restriction. These services provide a value added benefit as a source for differential corrections as well as integrity alerts and other information such as ionospheric mapping.
Such augmentation data generally originates from civilian sources. Ground based augmentation data may comprise local correction data, dependent on the user's distance to the reference receiver, and broadcast over a terrestrial link. Space based augmentation data may comprise regional correction data broadcast over a satellite link.
Military users typically do not have access to civilian augmentation data because military users require a higher degree of data validation and there is no defined mechanism to validate and authenticate civilian augmentation data.
Consequently, it would be advantageous if an apparatus existed that is suitable for sufficiently validating and authenticating augmentation data for military use.